1. Field of the Invention
The present invention relates to a semiconductor device and, more particularly, to an off-chip driver circuit and an output circuit using the same.
2. Discussion of Related Art
In designing integrated circuits (ICs) such as a memory chip, an off-chip driver circuit is used to transfer data information from the memory chip to external environments. In general, the off-chip driver circuit functions to transfer an internal data signal of a chip to external system environments at possible high speed.
A data output circuit having an off-chip driver circuit according to a prior art will be described with reference to FIG. 1, which shows a block diagram schematically illustrating the configuration of a data output circuit 10 having an off-chip driver circuit in a related art.
The off-chip driver circuit 100 includes off-chip drivers 100-1 to 100-N. Each of the off-chip drivers 100-1 to 100-N uses the same data signal as one input and corresponding first to Nth control signals (N is a natural number of 2 or more) as the other input. Each of the off-chip drivers 100-1 to 100-N functions to reflect a possible difference in the performance of a device according to process conditions performed. Furthermore, each of the off-chip drivers is connected correspondingly to output driver within an output driver circuit 300. If a corresponding off-chip driver is turned off, an output driver connected thereto is turned off, and if a corresponding off-chip driver is turned on, an output driver connected thereto is turned on.
If an off-chip driver circuit operates in a high frequency state, however, data signals outputted from the off-chip driver circuit are turned on/off at the same time. It is therefore not technically easy to make an output (Dout) waveform of the output driver circuit 300 having an adequate slew. For example, in products such as a double data rate (DDR), etc. for implementing an ultrahigh speed operation, slew of an output waveform may become great and overshoot may thus take place. This causes the properties of a system interface to be significantly degraded.